This application is based on application No. 10-282575 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to image reading apparatuses, scanners, such as copiers, printers, facsimile, combinations thereof, microfilm readers, and image reading methods applied to such apparatuses and scanners. In particular, the present invention relates to apparatuses and scanners using a photoelectric conversion unit with limited pixel count to read images with high resolution, and image reading methods thereof.
2. Description of the Related Art
Conventionally an image reading apparatus has been known which employs a CCD linear sensor as an imaging device. Referring to FIG. 13, the conventional image reading apparatus is comprised of an automatic document feeder (ADF) 1 feeding a plurality of set original sheets onto a platen 3 one by one, a lamp 5 illuminating with light an original placed on platen 3, mirrors 7a-7c for directing a light reflected from the original to a lens 9, lens 9 for focusing the reflected light on a CCD linear sensor 11, and CCD linear sensor 11 for receiving and converting the reflected light into an electrical signal. CCD linear sensor 11 has photoelectric conversion elements arranged in a main-scanning direction (a direction perpendicular to the plane of the figure) and transmits to a control unit 80 the information of one line of the original as an image signal. Lamp 5 and mirror 7a are supported by a movable portion 6. Mirrors 7b and 7c are supported by a movable portion 8. Lens 9 is supported by a fixed portion 10. Movable portion 6 is moved by a dive motor 17 in a sub-scanning direction (a lateral direction in the figure). As movable portion 6 moves in the sub-scanning direction, that portion of the original which is illuminated by lamp 5 varies. Thus, the original can be scanned by CCD linear sensor 11 in the sub-scanning direction. Movable portions 6 and 8 are also moved by drive motor 17 parallel to the sub-scanning direction to provide a constant distance traveled by the lamp 5 light from the light""s reflection at the original to the light""s arrival at CCD linear sensor 11.
Thus the conventional image reading apparatus uses dive motor 17 to move movable portion 6 in the sub-scanning direction to allow CCD linear sensor 11 to load an image for each line successively.
In the image reading apparatus, however, CCD linear sensor 11 has a fixed number of photoelectric conversion elements (pixels) arranged in the main-scanning direction and the resolution of loaded image data in the main-scanning direction thus depends on the pixel count of CCD linear sensor 11 and thus has a fixed value. Thus, in the conventional image reading apparatus, the resolution in the main-scanning direction depends on the performance of CCD linear sensor 11 and can thus not be improved.
The present invention has been made to overcome the disadvantage described above.
One object of the present invention is to provide an image reading apparatus and scanner capable of reading images with high resolution via a photoelectric conversion unit with limited pixel count, and an image reading method thereof.
To achieve the above object, the present invention in one aspect provides an image reading apparatus including a photoelectric conversion unit having photoelectric conversion elements arranged in a main-scanning direction for receiving a light reflected from an original, a unit for providing a relative displacement in the main-scanning direction between a light receiving surface of the photoelectric conversion unit and an object""s image formed on the light receiving surface of the photoelectric conversion unit, and a control unit disposed to time charge accumulation in the photoelectric conversion unit, wherein the unit providing a relative displacement provides the displacement according to a predetermined oscillation function and the control unit uses a distance from a center of an amplitude of the relative displacement to the photoelectric conversion unit and a time period of charge accumulation by the photoelectric conversion unit to determine a time point to start charge accumulation.
The present invention in another aspect provides a scanner including a photoelectric conversion unit having a plurality of photoelectric conversion elements arranged in a predetermined direction, an optical system focusing a light reflected from an original onto the receiving surface of the photoelectric conversion unit, and a drive unit providing a relative positional displacement in a predetermined direction between the photoelectric conversion unit and an image formed on the light receiving surface of the photoelectric conversion unit via the optical system.
The present invention in still another aspect provides an image reading method of focusing a light reflected from an original on a light receiving surface of a photoelectric conversion unit having a plurality of photoelectric conversion elements arranged in a first direction, and moving the formed image and the light receiving surface relative to each other in a second direction crossing the first direction while reading an image of the original, including the steps of providing a relative positional displacement in the first direction between the photoelectric conversion unit and the image formed on the light receiving surface of the photoelectric conversion unit via an optical system, and allowing the photoelectric conversion unit to perform charge accumulation at its displaced position and output an image signal.
Thus, the present invention can provide an image reading apparatus, scanner and image reading method capable of reading images with high resolution via a photoelectric conversion unit with limited pixel count.